Wireless communications services and portable devices that use such services continue to increase in popularity. The wireless networks and mobile devices support a wide array of voice and data communication functions. A key feature of such devices and the wireless networks is mobility, that is to say, the ability of the user with the device to move freely from place to place and still operate the device to obtain wireless network services.
The capability of a cellular network to manage the movement of User Equipment (UE) within the cellular network is referred to as mobility management. The network device that manages UE mobility management in a radio access network (RAN), such as a Long Term Evolution (LTE) RAN network, may be referred to as a mobility management entity (MME). The MME uses identifiers related to the respective UEs as well as various identifiers related to the cells in which the respective UEs are located and/or the cells that UEs may next roam into. The cellular services within the cells are provided by base stations that provide the cellular services to the UE over an air interface. As the UE travels from one cell to another, the MME manages the delivery of cellular services to the respective UE. In order to efficiently manage the delivery of cellular services, each base station is assigned an identifier which a serving MME tracks in order to reach out to an idle UE. The general indication is a tracking area, which refers to a location being serviced by a base station. The purpose of a tracking area designation is so the MME does not have to scan an entire network to locate a UE. A tracking area may identify one or a group of cells. The UE assists the MME by reporting to the MME TA in which the UE is located. In addition, the UE maintains a list of TAs that were used or identified by the UE. For example, while idle the UE may detect base station reference signals and read overhead messages transmitted by the detected base station. The overhead messages include identifying information of the respective base stations. In addition, the UE may make measurements, such as received signal strength, of the respective reference signals. The identifying information in the overhead messages and the respective measurements may be stored by the UE for future use.
One of the identifiers included in the overhead messages is a tracking area identifier (TAI). In general, TAIs are identifiers of areas in which a UE has been serviced by one or more radio base stations, such as an evolved Node B (i.e., eNB). The number of TAIs is limited because each cellular provider only has 65535 tracking area codes available, and usually a large number of the TAIs are pre-allocated to the tracking areas (TAs) of the cellular provider to accommodate tracking areas that correspond to fixed eNBs; therefore, a small pool of TAIs is available for the more mobile HeNBs. As a UE travels closer to another eNB, a determination is made whether the UE would be better served (i.e., receive better quality of service) from a neighboring or target eNB as compared to the service that the UE is currently receiving from the serving, or source, eNB. The source eNB may make a determination that UE is better served by a neighboring eNB. The MME is informed via a handoff request of the impending eNB change from a source eNB identified by a first TA to the target eNB of a second TA. The transfer of service from the source eNB to the target eNB is referred to as a “handover.” In case the source and target eNBs have different TAIs, a Tracking Area Update (TAU) procedure may get initiated by the UE so that the MME can update and store the new location (i.e., TAI) of the UE. This will help the MME to reach out to an idle UE based on the UEs last known location or TA in case some data needs to be delivered to that UE.
The handover process is covered by telecommunication standards, such as the current standard (i.e., 3GPP Release 12 (R12)). At a high level and according to the standard, there are three broad processes that constitute handover: 1) handover preparation, 2) handover execution, and 3) handover completion. The particular handover process discussed herein is a preliminary operation related to the handover preparation. After the handover preparation process discussed herein, the two other handover operations, handover execution and handover completion, that make up the broader handover operation occur. The handover execution and handover completion processes are unaffected by the improvements to the handover preparation discussed in the detailed description of the examples.
Similar to the revolution in UE devices becoming more powerful yet more compact, devices that offer the substantially the same functionality as the base stations described above are also becoming more powerful and compact. These base station-like devices, referred to as Home eNBs (HeNBs) are portable, provide cellular services to multiple UEs, and may be installed by consumers via an internet connection to a cellular service provider server. Once the HeNB is provisioned with the recommended parameter settings provided by a cellular service provider server, the HeNB provides an air link to the cellular communication network of the cellular service provider to which the UE may attach, and receive cellular service. The HeNB communicates with the MME in the same manner as an eNB. In effect, the HeNB is another eNB in the cellular network. As a result, the MME has to manage and service the UEs that may be in the area of the HeNB. The HeNBs typically provide cellular services to a small coverage area, often referred to as a femtocell. These femtocells are small geographical areas, and are typically in areas where cellular service from an eNB is poor, such as indoor locations, such as a building or urban canyon that are also not high UE traffic areas and the like. However, an HeNB may begin providing services within a coverage area of an eNB. As such, the HeNB falls substantially in the TA of an eNB.
A TA is identified by a tracking area identifier (TAI). The TAI of each base station, eNB and HeNB, under control of the MME is provided to the MME. There are a limited number of TAIs. The implementation of the TAI management concept did not take into account the implementation of HeNBs. As such, the type and deployment strategy for HeNBs is different and leads to a problem with the limited TAIs. A HeNB is a small scale shorter range device intended for deployments in users/customers premises (homes, offices, or the like). As a result, HeNBs are likely to be deployed in larger numbers and the cellular service provider is less likely to be able to control or know of the geographic coverage area such HeNBs provide. An MME routing the handover signaling messages based primarily on the TAI of the target HeNB would tax the limited TAI resources of the cellular service provider.